This invention relates to a heat-recoverable soldering device having a solder insert and associated therewith, a temperature indicating solder flux composition, and to methods of soldering using said use of devices. It further relates to certain novel temperature indicating solder flux compositions and to the use of such compositions in soldering.
Heat-recoverable solder devices are known in the art. See, for example, U.S. Pat. Nos. 3,316,125 to Sherlock, 3,305,625 to Ellis, 3,316,343 to Sherlock, 3,396,460 to Wetmore and 3,396,894 to Ellis. Such heat-recoverable devices are generally heat-shrinkable polymeric sleeves having a fusible insert comprising solder. Elongate substrates, such as a pair of wires, are inserted into the sleeve and heat is applied causing the sleeve to shrink into contact with the substrates. The heat also causes the solder to melt and flow around the substrates. Upon cooling, a solid solder joint is formed between the substrates. In general, the temperature required to melt the solder is higher than the temperature required to shrink the sleeve. Thus, visual observation that the sleeve has completely recovered does not necessarily mean that the temperature necessary for soldering has been reached. There is, therefore, no visible indication during the soldering process that enough heat has been applied. Further, in the event that a soldered joint so formed fails during use, there is no way of subsequently inspecting the joint to determine whether the failure was due to inadequate heating during the soldering process.
This invention provides a direct, positive indication that a solder joint or connection has reached the correct soldering temperature. It provides this indication during the soldering process to indicate when adequate heat has been aplied to effect the solder termination. Further, it provides a continuing indication after the soldering step has been completed, that adequate heat was applied during soldering. In a preferred embodiment, the completed soldered joint can be visually inspected to detect improperly formed terminations.